Mixing valves in hot water heater systems are generally used to increase the hot water capacity of hot water tanks of the hot water heaters. By increasing the temperature of the hot water in the hot water tank, and then mixing the hot water flow from the hot water tank with cold water in a mixing valve, the realized capacity of the hot water tank is increased.
U.S. Patent Application Publication No. 2014/0026970, filed Jan. 30, 2014, entitled “Electronic Mixing Valve in Standard Hot Water Heater”, and which is incorporated by reference in its entirety herein, discloses electronic mixing valves for use in hot water heaters. Electronic mixing valves generally provide improved control over the temperature of the water delivered from associated hot water heaters relative to, for example, mechanical mixing valves.
However, improvements could be made to presently known methods for controlling such electronic mixing valves. For example, improvements to the response time for outputting a desired water temperature from a hot water heater that utilizes an electronic mixing valve could be advantageous. Many presently known electronic mixing valves are operated by controllers which utilize proportional, integral and derivative gains and temperature tolerances when controlling electronic mixing valves. Further, many such controllers currently utilize only one set of predefined variables, such as gains and/or tolerances, for all valve operations and requested temperature setpoints. In some cases, such as low flow rates or high temperature set points, the use of predefined variables can lead to these controllers and electronic mixing valves encountering unstable conditions and entering oscillatory states.
Further, many presently known hot water heaters which utilize electronic mixing valves can encounter hot water “spikes”, when the electronic mixing valve is fully opened, which can lead to scalding, etc. The risk of such spikes can occur in situations wherein, for example, the hot water heater is “idle” for a period of time and the water encountered by a temperature sensor that measures output temperatures from the electronic mixing valve thus cools down. Additionally, in other situations, such hot water heaters can also encounter cold water “spikes”.
Accordingly, improved hot water heater systems and methods for controlling electronic mixing valves are desired. In particular, improvements which reduce the risk of the electronic mixing valves encountering unstable conditions and entering oscillatory states would be advantageous. Further, improvements which reduce the risk of hot water and cold water “spikes” would be advantageous.